The monoclonal antibody 14.27 reacts with rat CD38, also known as ADP-ribosyl cyclase. CD38 is a type II transmembrane glycoprotein that is an ectoenzyme that catalyzes the synthesis and hydrolysis of cyclic adenosine diphosphate ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP). cADPR and NAADP are secondary messengers involved in calcium mobilization. CD38 can also act as a receptor for CD31 or agonist monoclonal antibodies. CD38 is expressed by leukocytes, early hematopoietic precursor cells, epithelial cells, astrocytes, some muscle cells, kidney cells, and thyroid cells. CD38 plays a role in the production of pro-inflammatory cytokines, proliferation, cell activation, cell migration, cell adhesion, and protection from apoptosis.